フランジ応力制御による湾曲骨格部品のねじれスプリングバック抑制技術

抄録

A defect in the dimensional accuracy caused by springback is a major problem in sheet metal forming of high-strength steel sheets. In particular, ensuring dimensional accuracy of a long curved part is difficult owing to twist springback, which leads to complex three-dimensional surface variation. In this study, a new forming method for reducing twist springback was developed by focusing on stress at the flange, which is a cause of twist springback. The developed forming consists of two forming processes. In the first process, the flange part of the blank is sloped owing to the gap between the upper die and the flange-forming die, which are set at a lower position at height h relative to the punch. In the second process, the flange part of the blank is formed into the target shape by the flange-forming die, and the slight reverse strain that contributes to stress reduction at the flange. Experiments of press forming of a simple curved part and an actual automotive part using high-strength steel sheets were carried out. The experimental results showed that twist springback varied with the height h of the flange forming die. It was experimentally proven that twist springback can be minimized by the developed forming.